Formation of high purity Si nanofiber from metallurgical grade Si by molten salt electrorefining

We studied the purification of metallurgical grade Si from solutions of K₂SiF₆ in fluoride melts using a molten salt electrorefining process at 700 °C. Electrorefining close to the deposition potential gave dense, coherent, and well-adherent deposits. It was shown that the deposition rate and microstructure of Si strongly depend on the process temperature. Deposited polycrystalline silicon has a well defined rod shape and crooked structure that varies with current density. The anodic dissolution rate is affected by the initial concentrations of K₂SiF₆ and the applied current density. The results of an inductively coupled plasma (ICP) analysis indicated that recovered silicon fiber deposits with purities greater than 99.98% can be obtained using the developed technique. The morphology of the electrodeposited silicon on silver substrates is discussed in the context of a cathodic reaction on the electrode surface, and a comprehensive explanation of the purification mechanism with salt removal is provided.     

Preparation of zirconium-based ceramic and composite fine-grained powders

Zirconium-based ceramics and composites such as ZrC, ZrB₂, ZrC-SiC, ZrB₂-SiC-ZrC, and ZrB₂-SiC-ZrC-ZrSi were synthesized in fine powder form via combustion synthesis (CS) using ZrSiO₄, Mg, C, B, and NaCl as raw materials. Temperature distributions in the combustion wave were measured by thermocouples and used to estimate the combustion temperature and wave propagation velocity. The influence of the NaCl mole fraction on the combustion parameters, phase composition, and particle size of the composite powders was investigated. The experimental results revealed that the combustion temperature and particle size of the composites have a stable decreasing tendency with increase in the NaCl mole fraction in the starting mixture. It was found that near the combustion limit (1.5 mol NaCl), the combustion temperature drops below 1500 °C and the particle size reaches the nanometer scale.     

Cataract halos: a driving hazard in aging populations. Implication of the Halometer DG test for assessment of intraocular light scatter

OBJECTIVE AND BACKGROUND: Cataract, regardless of etiology, results in light scatter and subjective glare. Senile cataract is emerging as a crucial factor in driving safely, particularly in night driving and adverse weather conditions. The authors examined this visual impairment using a new Halometer DG test in the eyes of older adult drivers with and without cataract. METHOD: Examined subjects consisted of n=65 older adults with cataract in one or both eyes and n=72 adult drivers who did not have a cataract in either eye. Subjects were examined for distance high contrast visual acuity (VA) and red/green disability glare (DG) with a new halo generating instrument. Subjects also completed a subjective Driving Habits Questionnaire (DHQ), designed to obtain information about driving during the past year. RESULTS: DG increased with age of the driver. VA and Halometer DG testing of better and worse eyes prognosticated impairments which significantly affect driving performance. Cataract subjects demonstrated increased Halometer DG scores and were two to four times more likely to report difficulty with driving at night and with challenging driving situations than were cataract-free drivers. CONCLUSION: DG is a specific cataract-induced functional age-related risk factor of driving difficulty, easily measured by a technician with a new Halometer DG device. APPLICATION: Optometrists and ophthalmologists should incorporate Halometer DG testing in their pre-examination vision testing rooms for patients over age 55, and also perform this test on others who complain about glare. Traffic safety engineers should incorporate automotive optical-microprocessor-aided tests for DG into cars, to alert drivers of mild functional impairments and progressive degrees of DG sensitization.     

Metal-enhanced fluorescence of chlorophylls in single light-harvesting complexes

Ensemble and single-molecule spectroscopy demonstrates that both emission and absorption of peridinin-chlorophyll-protein photosynthetic antennae can be largely enhanced through plasmonic interactions. We find up to 18-fold increase of the chlorophyll fluorescence for complexes placed near a silver metal layer. This enhancement, which leaves no measurable effects on the protein structure, is observed when exciting either chlorophyll or carotenoid and is attributed predominantly to an increase of the excitation rate in the antenna. The enhancement mechanism comes from plasmon-induced amplification of electromagnetic fields inside the complex. This result is an important step toward applying plasmonic nanostructures for controlling the optical response of complex biomolecules and improving the design and functioning of artificial light-harvesting systems.     

Electrochemical behavior of Nd in its pyrometallurgical recovery from waste magnet

High-purity Nd metal was recovered from waste Nd–Fe–B magnet by the molten salt electrowinning process with chemical pretreatment. X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), cyclic voltammetry(CV),chronopotentiometry(CP), and inductively coupled plasma-atomic emission spectrometer(ICP/AES) were used to characterize the deposit and electrochemical behaviors. The results show that NdF3 is effectively synthesized from the Nd–Fe–B magnet using HCl solution and NH4F. During the chemical treatment of the waste magnet,iron impurity is eliminated as a soluble [NH4]3[FeF6]complex. Electrowinning using NdF3 in LiF molten salt shows that Nd metal is deposited from the electrolyte onthe cathode at the reduction potentials ranging from-1.48to-1.35 V(vs. W) with the concentration change of NdF3.The final purity of Nd metal deposit is higher than99.78 %.     

Preparation of porous silver particles using ammonium formate and its formation mechanism

Here we report the preparation of two different types of macroporous silver particles (round and coral) by simple chemical reduction using ammonium formate. We also discuss the chemical mechanism of silver particle and macroporous silver particle formation. The synthesized round type and coral-type porous silver particles were 20–50 μm and 30–150 μm in size and their pores were 100–200 nm and 1–2 μm across, respectively. They were characterized by particle distribution analysis, X-ray diffraction, and scanning electron microscopy.     

A macrokinetic study of the WO3/Zn reaction diluted with NaCl

In this work, experiments with stoichiometric WO₃ + 3Zn mixture, diluted with NaCl, were conducted for nanostructured tungsten synthesis. The reaction samples, preheated until 720 K, were self-ignited and reacted in the steady combustion regime. The temperature–time profiles in the combustion wave were collected over the NaCl interval from 1 to 6 mol, and the values of the combustion parameters (T_c, U_c) were evaluated. From these profiles the spatial distributions of heat generation rate (x) and degree of conversion η(x) in the combustion wave were received at different k values. The calculated activation energy for the combustion process was E = 55 ± 2 kJ mol⁻¹. After the reduction experiments, pure tungsten nanopowder with particle size from 200 to 50 nm was obtained depending on NaCl concentration.